JP11-063147 published by the Japanese Patent Office in 1999, discloses a continuously variable power-split transmission for a vehicle. This continuously variable power-split transmission is provided with a toroidal continuously variable transmission mechanism (variator) and a fixed speed ratio transmission mechanism having identical rotational inputs. The outputs of these transmission mechanisms are input into a planetary gear mechanism. When the vehicle is running in a high speed mode, the rotational output of the planetary gear mechanism is applied for driving the wheels of the vehicle, and when the vehicle is running in a low speed mode, the rotational output of the variator is applied for driving the wheels of the vehicle, thereby enlarging the speed ratio range and achieving a high power transmission efficiency.
In this continuously variable power-split transmission, all of the rotational input in low speed mode passes through the variator, and therefore the power transmission efficiency in low speed mode cannot exceed the power transmission efficiency of the variator. Further, since all of the rotational input in low speed mode passes through the variator, a variator with a large transmission torque capacity is required, and as a result it is difficult to reduce the size of the variator.